Hi all,
I tried a search, but couldn't find a similar issue that provided a cure so here goes:

Some of you may remember the saga of my "no spark" issue I had a while back. Finally got that corrected and the car is up and running. Since then, and I must stress this is only since the ignition problem, I've been having issues with the idle.
It will start up and run/drive normally until it gets up to operating temp, then the problems start. It continues to drive just fine, plenty of power for a 305, only issue is when at a stop light or heavy traffic. It will idle ok for about a minute, then the RPM will drop, nearly stall, then jump back to life. The RPMs will surge up to 1500 or so then go back to idle. The RPMs will continue to fluctuate between normal idle and 150-250 rpms, again surging back everytime. IF the car is in neutral or park it idles slightly better, but will often quit when you put it in gear. It will almost always stall after about 30-40 seconds of the idle fluctuating.
Fuel pressure is 43psi with key on, engine stopped. I waited about 30 minutes and hadn't lost any pressure so my pressure is good, and the injectors aren't leaking (the injectors are Ford 19 lb/hr). With the engine running, fuel pressure stays right about 38-39 psi and will actually increase to 40-41 as the engine tries to stall then drop back down as the engine starts to run normally. I didn't drive it with the fuel pressure gauge connected so I don't have those readings. I can't find any vacuum leaks, but haven't put a gauge on yet to see how much vacuum its pulling. It doesn't seem to have a miss either.
Its been suggested that this is a fuel issue, and while I'm not ruling anything out yet, my fuel system has tested ok so far unless someone would like to suggest another test I haven't tried. I'm thinking this is ignition related, as the problem has only surfaced since having ignition troubles. I'm running a reman dizzy I got at Autozone, new (stock replacement) coil, Accell cap, rotor, and wires, and Delco plugs. The cap, rotor, wires, and plugs while old (5+ years) have <5000 miles on them. I'll be replacing them regardless in a couple weeks as money allows.
Any other thoughts/suggestions?

Thanks for reading!

Dave

 

Dave,
Check your IAC (Idle Air Control) sensor and see if it has carbon all over it. Usually this sensor will cause issues similar to what you described.

Hope this helps.

 

IAC, yeah, forgot to mention that I replaced it last saturday with one I pulled from the local boneyard off a 91 Z28. I cleaned it up real good and while I was at it, I removed and thoroughly cleaned the passages in the throttle body. No results.

Dave

 

I'm having similar problems. Only difference now is that I've dealt with the surge/stall for a couple months now, and now, if it stalls it wont start again. I have to let it sit, or cycle the key. Hit or miss if it starts

 

So far so good, mine always starts back up. I put a vacuum gauge on it the other day and it pulling about 19in at idle, but it drops to 13-15 when the idle drops, so I definitely think there;s a vacuum leak somewhere.